(This is also at https://bugs.launchpad.net/kicad/+bug/1455345)
Minimal example screenshot: http://u.forre.st/u/fiyaqxjg/drc.png Minimal example board file: http://u.forre.st/u/kjzegyao/drc.kicad_pcb Two pads (one a circle and one an oval) cause a false DRC violation in certain arrangements. I am reasonably certain that this is due to the rectangle part of the segment-oval test in DRC::checkClearanceSegmToPad. This function is called by DRC::checkClearancePadToPad with the circle pad having been transformed to a zero-length segment and the oval pad remaining as is. Then, DRC::checkClearanceSegmToPad looks at the oval pad as two circles and a rectangle, testing the segment against each, grown according to the segment's width and the clearance. The rectangle is grown at each end of its short axis by half the width of the segment (the radius of the circular pad in this case) plus the clearance (which makes sense) and grown at each end of its long axis by half the width of the segment (!!!). Growing the rectangular part of the pad along its long axis by anything is wrong because the dilation of a rectangle is a rounded rectangle, but by growing it along both axes, we form a shape that is bigger than what it should be (it has corners that shouldn't be there). We don't need to grow it along its long axis at all, because intersections near the ends of the pad are taken care of by the circle tests. A patch that fixes this issue, as I see it, is here: diff --git a/pcbnew/drc_clearance_test_ functions.cpp b/pcbnew/drc_clearance_test_ functions.cpp index 87acf72..af5f78d 100644 --- a/pcbnew/drc_clearance_test_ functions.cpp +++ b/pcbnew/drc_clearance_test_functions.cpp @@ -897,9 +897,9 @@ bool DRC::checkClearanceSegmToPad( const D_PAD* aPad, int aSegmentWidth, int aMi // Test the rectangle area between the two circles m_xcliplo = m_padToTestPos.x - seuil - padHalfsize.x; - m_ycliplo = m_padToTestPos.y - segmHalfWidth - deltay; + m_ycliplo = m_padToTestPos.y - deltay; m_xcliphi = m_padToTestPos.x + seuil + padHalfsize.x; - m_ycliphi = m_padToTestPos.y + segmHalfWidth + deltay; + m_ycliphi = m_padToTestPos.y + deltay; if( !checkLine( startPoint, endPoint ) ) { Note that the reason that this hasn't been noticed until now even though DRC::checkClearanceSegmToPad is used to check traces against pads is that the effect of this bug is vanishingly small unless the segment (here being the circular pad) is much larger than the pad (here being the oval pad). Indeed, I can trigger the same bug with a big enough segment and the same oval pad: http://u.forre.st/u/yftulnmj/drc2.png http://u.forre.st/u/bnfxrhwc/drc2.kicad_pcb _______________________________________________ Mailing list: https://launchpad.net/~kicad-developers Post to : [email protected] Unsubscribe : https://launchpad.net/~kicad-developers More help : https://help.launchpad.net/ListHelp
